abstract class Animal {
  abstract eat(): void ;

  abstract run(): void ;

  abstract work(): Array<string> ;
}

class Dog extends Animal{
  constructor() {
    super();
  }

  eat(): void {

  }

  run(): void {
  }

  work(): Array<string> {
    return undefined;
  }
}

class xiaonaiGou extends Dog{


}

new xiaonaiGou().eat();
